The present invention relates to the refurbishment of sputtering targets.
A sputtering chamber is used to sputter deposit material onto a substrate to manufacture electronic circuits, such as for example, integrated circuit chips and displays. Typically, the sputtering chamber comprises an enclosure wall that encloses a process zone into which a process gas is introduced, a gas energizer to energize the process gas, and an exhaust port to exhaust and control the pressure of the process gas in the chamber. The chamber is used to sputter deposit a material from a sputtering target onto the substrate. The sputtered material may be a metal, such as for example, aluminum, copper, tungsten, titanium, cobalt, nickel or tantalum. The sputtered material may also be a metal compound, such as for example tantalum nitride, tungsten nitride or titanium nitride. In the sputtering processes, the sputtering target is bombarded by energetic ions formed in the energized gas, causing material to be knocked off the target and deposited as a film on the substrate. The sputtering chamber can also comprise a magnetic field generator that shapes and confines a magnetic field about the target to improve sputtering of the target material.
In these sputtering processes, certain regions of the target are often sputtered at higher sputtering rates than other regions resulting in uneven sputtering of the target surface. Uneven target sputtering can arise from the complex contoured magnetic field maintained about the target to confine or stir energized gas ions about the target surface. Uneven sputtering can also be related to differences in grain size or structure of the target material, chamber geometry, and other factors. Uneven sputtering of the target forms sputtered depressions in the target such as pits, grooves, race-track like trenches, and other recesses, where material has been sputtered from the target at a higher rate than the surrounding areas. The development of these depressions can be undesirable because very deep features can penetrate the target to expose chamber components, such as backing plates, behind the target. Sputtering from the backing plate can contaminate the substrate being processed. Recessed features that are very large or very deep can also affect the deposition uniformity of sputtered material on the substrate.
Accordingly, unevenly sputtered targets are typically removed after processing of a predefined number of substrates and before the uneven sputtered depressions become too deep or wide. The sputtering target is then discarded, or more typically, re-used when the target material is expensive or has a high purity level that is difficult to obtain. For example, the target can be re-used by melting down the sputtered target material and shaping a new sputtering target. However, melting down and re-shaping the target is costly because it requires re-forming the entire target.
Several methods have also been developed to refurbish a sputtering target. In one method, the excessively sputtered regions of the target are filled with a powdered sputtering material and a laser or electron beam is directed onto the powdered material to melt and bonds the powdered material to the target, as for example, described in U.S. patent application No. 2002/0112955 to Aimone et al, filed on Feb. 14, 2002, which is herein incorporated by reference in its entirety. However, the laser or e-beam method requires expensive electron or laser beam sources and tracking or scanning equipment to follow the contour of the sputtered depression. Also, for certain materials, such as for example, high temperature refractory metals such as tantalum, the laser or e-beam source has to have an excessively high wattage that can cause re-crystallization or other changes in the regions of the target that are adjacent to the sputtered depression regions. Voids or bubbles can also form in the powdered material due to insufficient melting or when the molten material has a viscosity that is too high to fully penetrate the small scooped out regions within the sputtered depressions of the used target. Applying heat to the powdered material already filling the sputtered depressions can also cause the surface layer of powered material to melt before underlying layers are melted, resulting in subsequent out-gassing and a resultant pore structure in the filled depression.
Thus, it is desirable to have a method of refurbishing a partially sputtered used target to fill in sputtered depression features formed in the target. It is also desirable to refurbish the eroded regions without damaging or otherwise altering the crystal structure of adjacent regions of the target. It is further desirable to have a method of refurbishing a target that is not excessively costly and that can efficiently refurbish targets.